The key tool to handle PSIs in dimensional regularization is a generalization of spherical
integration to arbitrary dimension. In our consideration we follow handbook [1]}.
For any integer \(n\) -dimension we can introduce spherical coordinates. For \(n=2\)  dimension we have
\(\vec{x\,}^{(2)}=r_2 \vec{u\,}^{(2)}(\theta _1)\quad \text{with}\quad \vec{u\,}^{(2)}(\theta _1)=(\sin \theta _1,\,\,\cos \theta _1) \, ,\) 
